The present invention relates to a method of manufacturing a semiconductor device for obtaining the semiconductor device by dividing a semiconductor wafer, on which a plurality of semiconductor elements are formed, into individual pieces of semiconductor elements. The present invention also relates to a cutting device of cutting the semiconductor wafer used in the manufacturing method.
A semiconductor device mounted on a board of electronic equipment is conventionally manufactured in such a manner that pins of a lead frame and metallic bumps are connected to semiconductor elements, on which a circuit pattern is formed in the state of a wafer, and the semiconductor elements are subjected to a packaging process in which they are sealed with resin. Since the size of electronic equipment has been recently reduced, the size of the semiconductor device has been also decreased. Especially, they have been actively making investigation into the reduction of the thickness of a semiconductor element.
The mechanical strength of the semiconductor element, the thickness of which is reduced, is so low that the semiconductor element is liable to break in the process of cutting conducted in the dicing step in which the semiconductor element in the state of a wafer is cut into individual pieces, and the yield of machining is inevitably lowered. Concerning the method of cutting the semiconductor element, the thickness of which is reduced, instead of the mechanical cutting method, a plasma dicing method is proposed in which the semiconductor wafer is cut when cutting grooves are formed by the etching action of plasma. Concerning this method, for example, refer to Patent Document 1.
[Patent Document 1]
Japanese Publication JP-A-2002-93752
However, in the process of plasma dicing of the prior art described above, the following problems are caused due to the want of uniformity of the plasma etching action. Further, these problems have not been solved yet. In the process of plasma etching, masking is previously conducted so that regions except for the cutting lines can be covered with a resist layer. The semiconductor wafer on which masking has been conducted is accommodated in the processing chamber of the plasma processing device, and only the regions of the cutting lines are exposed to plasma in the processing chamber so that silicon in the regions can be removed by means of etching.
In this connection, an etching rate showing the degree of etching conducted by plasma is not necessarily uniform. Therefore, the etching rate distribution fluctuates in the processing chamber. Accordingly, in the process of plasma dicing conducted in the processing chamber, silicon in the portions of the cutting lines, which are located in a range of a high etching rate, is more quickly removed than silicon in the other portions. Therefore, cutting is more quickly completed in a short period of time in these portions.
The cutting lines in these portions of the high etching rate, are successively exposed to plasma until silicon in the portions of the cutting lines located in regions of the low etching rate is removed. Accordingly, when silicon is completely removed from the regions of the high etching rate, the protective sheet on the lower face side of the semiconductor wafer is directly exposed to plasma.
When the plasma processing continues in the above state, heat generated by plasma directly acts on the protective sheet. As a result, there is a possibility that the protective sheet is overheated, burned and deformed. According to the conventional plasma dicing method, it is impossible to effectively prevent the protective sheet from being damaged by heat caused by the want of uniformity of the etching action of plasma.